In conventional practice, high-frequency power supply circuits used in high-frequency power supply apparatuses or the like for supplying high-frequency power to plasma generators or the like use linear amplifiers connected in multiple stages so that minute vibrations in internal liquid crystal oscillators are amplified to the final output. Such amplifiers use an amplification scheme known as linear amplification, which is an amplification scheme having a comparatively low efficiency of about 50%.
However, as semiconductor wafers and display panels or the like having transistors incorporated therein have both increased in size, plasma treatment apparatuses have also increased in size, and greater outputs have been required for the power sources for the plasma. In conventional low-efficiency amplifiers, the volume and lost power increase dramatically with increased output, and commercial demand has therefore not been satisfied. High-frequency power sources that use an amplification scheme known as switching-mode amplification and provided with higher efficiency (80% or more) than in the prior art have recently been put into use.